Hearing aid

ABSTRACT

The present invention relates to a hearing aid system comprising a hearing implant and a method of powering a hearing implant, the system comprising an external ear canal module and an implant, wherein the signalling and/or powering of the ear implant is by way of a light signal being provided to the implant through the ear drum from, for example, the ear canal module.

The present invention relates to a hearing aid system comprising ahearing implant and method of powering a hearing implant.

Sensorineural deafness is by far the most common type of hearing loss.Deafness affects 9 million people in the United Kingdom, of which about95% have sensorineural deafness (source Defeating Deafness, UnitedKingdom). Causes include congenital, bacterial, high intensity noiseand, especially, the ageing process, with 30 percent of those affectedbeing over 60 years. Hearing impairment is the third most common chronicproblem affecting the ageing population—and one of the least diagnosed.There is also an increased prevalence in some sections of the youngerage group, due to exposure to loud noise.

There are currently no effective means of repairing the cochlea or thenervous pathways to the brain. For most patients, hearing can berestored adequately by sufficient amplification of sound with a hearingaid. Hearing aids have a number of problems: acoustic feedback (becausethe microphone is very close to the speaker), inadequate sound quality,and discomfort due to occlusion of the ear canal. They also areundesirable from the social point of view, in that the appearance ofwearing a hearing aid can cause users to feel that they are seen to behandicapped. The alternative is an implantable device.

Middle ear implants provide mechanical amplification by vibrating theossicular chain. They are intended for patients with moderate to severesensorineural hearing loss, who still have residual hearing. They couldpotentially benefit up to 50% of all people with hearing loss. Cochlearimplants, the alternative, provide electrical stimulation to the nervesof the inner ear, but are suitable only for the profoundly deaf, as allresidual hearing is destroyed during their implantation. They are notfavoured where there are alternative solutions.

Middle or inner ear implants however require a power supply. A few useincorporated batteries, which although last several years, requirereplacement. This undesirably necessitates a further operation for thepatient. Other implants use wires through the skull and the rest useradiofrequency or inductively coupled methods. Nevertheless, radiofrequency modulated transmission uses complicated circuitry, iscumbersome and costly, and the implanted receiver module itself has aheavy demand on power. It also has to be approved under each country'sradiofrequency regulations. Inductively coupled transmission methods usetwo coils or one coil and one magnet separated in close proximity.However, problems include high power consumption, signal variations andbackground noise. Moreover, MRI compatibility can also be a problem withsome components.

It is an object of the present invention to obviate and/or mitigate atleast one of the aforementioned disadvantages and/or problems.

Broadly speaking the present invention is based on powering a middle orinner ear implant using a light signal.

In a first aspect the present invention provides a hearing aid systemcomprising an external ear canal module and an implant;

-   -   the external ear canal module comprising a microphone, a light        source, a power source and necessary electronic circuitry;    -   the implant comprising a photoreceiver actively coupled to a        hearing actuator; and    -   wherein in use, sound detected by the microphone of the external        ear canal module is converted and transmitted by the light        source as a modulated light signal, the modulated light signal        being detected by the photoreceiver of the ear implant and        converted to an electrical signal for driving the hearing        actuator.

The implant it will be understood is located within the middle or innerear, i.e the body side of the ear drum.

Advantageously the present system is such that the light signal may besufficient to not only provide the sound information, but also power theear implant. In this manner, the ear implant need not have its owninternal power source. Alternatively or additionally a further lightsource may be used to charge a battery within the ear implant so as toprovide additional power to the implant.

Thus, in a further aspect, the present invention provides a method ofpowering and/or signalling an ear implant comprising transmitting alight source, or sources through a patients ear drum, such that saidlight source(s) is/are received by the ear implant and wherein saidlight source(s) is/are capable of powering and/or signalling the earimplant.

The components of the external ear canal module are typically containedwithin a single housing which is shaped to fit within the external earcanal. The microphone is positioned within the housing such that in useit can easily detect sounds. Thus, the microphone is generally arrangedto be directed towards the outside of the ear for receiving sound. Thesound received by the microphone is transduced by appropriate meansknown to those skilled in the art, into an electrical signal which inturn is converted into a modulated signal by suitable modulating means.The modulated signal is then output as a modulated light signal from thelight source.

The light source may be for example a light emitting diode (LED) and thelight signal itself may be visible light or preferably near infrared(NIR) light or infrared (IR) energy. Studies have shown that IR lightcan penetrate over 15 mm of tissue at frequencies up to 30 KHz. Thelight which is output by the module is to be received by the middle-earimplant. Thus, the light source is arranged in use so as to emit thelight in the direction of the photoreceiver. The light source thereforeemits the light towards and through the ear drum for detection by thephotoreceiver.

The skilled addressee is well aware of the electrical circuitry requiredfor the module and a power source, typically a battery, rechargeable orotherwise, is required to power the components of the module.

Although generally designed to fit snugly within the external ear canalso as to not easily fall out, the module should conveniently notcompletely occlude the ear canal. In this manner a channel, valve or thelike may be provided in the module so as to provide a passage throughthe module thereby preventing blockage of the ear canal. It isunderstood that such a channel valve or the like could be associatedwith the housing of the module and, for example, a channel could be cutinto the external surface of the module.

The implant may be an integrated photoreceiver/actuator unit such as amicro electromechanical system (MEMS)-integrated photoreceiver/actuator.The photoreceiver/actuator may be a single unit, or the photoreceiverand actuator may be separate and electrically connected by wiring. Thephotoreceiver may be a photo-sensitive diode, photo voltaic cell orother type of photoreceiver which may be located anywhere in the middleear, providing it can receive light generated from the light source ofthe ear canal module. It may be covered by a biocompatible coating,which could include coverage of the photoreceiver.

In order that a patient suffers no or minimal residual hearing loss, theimplant may sit on the ossicular chain, rather than linking to it from aremote fixation, such that the only additional mechanical impedance isdue to the small mass of the actuator itself. Locating the actuator onthe ossicular chain may also help to eliminate any post-operativealterations to implant performance from tightening or loosening of theactuator-ossicle coupling during the healing of swollen tissues, andfrom small displacements arising from the altered gravitational effectsof lying down during the operation and sitting/standing up afterwards.

The actuator may, for example, be located on the incus long process, theincudostapedial joint (which could be disarticulated temporarily withoutdamage for the fitting of an annular shaped actuator) or the stapes. Theactual design of the actuator will be determined by the skilledaddressee according to the location selected, an important aim being toreduce acoustic feedback An alternative position may be in the innerear, for example the promontory, where coupling may be direct, viafenestration: a surgical technique to create a window in the inner earin order to contact the inner ear fluid directly, or using an externalanchoring support.

The actuator may be secured in place by methods such as cementing,grafting or mechanical means, for example screws or barbs. It could beosseointegrated with the ossicular chain.

Actuation may be mechanically driven or electrical. In the middle ear,actuation will generally be mechanical vibration of the ossicular chain,or more specifically individual bones thereof. If the actuator is placedin the inner ear, actuation may be carried out mechanically by forexample direct or indirect vibration of the perilymph fluid in the innerear, or electrically to an electrode or electrode array, coupled forexample to the cochlea.

In order to drive a mechanically operated actuator, light is received bythe photoreceiver, which is in turn converted into an electrical outputwhich drives the actuator resulting in vibrations. Typically theactuator may be a thin disk made of piezo ceramic material such as leadzirconate titanate (PZT), or lead lanthanum zirconate tibanate PLZT.This is desirable because the materials are magnetic resonance imaging(MRI) compatible, as well as being efficient transducers. Additionallymore than one disk may be provided in a desired configuration and/ordisk may be more than one layer thick. The vibrations may also begenerated using for example a disk(s) of piezo ceramic in conjunctionwith a flexible diaphragm of for example stainless steel, titanium, oraluminium.

Furthermore, the use of a flexible diaphragm permits hydraulicamplification to increase the displacement of the flexible diaphragm.For example, an increase in the displacement of the flexible diaphragmcan be obtained using a simple fluid-filled tube coupled to a largerdiameter disk actuator which is located at the opposite end of the tubefrom the flexible diaphragm and may contact for example the perilymph.Such a tube structure allows the actuator module to be placed in themiddle ear cavity which provides more space for accommodation andsupport.

As an example, a PZT disc actuator now in use in an incus-driven middleear implant operates at 1V and 100 μA. This power requirement could begenerated from the photodetector without the need for further electronicamplification. Passive RC filtering could be used for demodulation. Incase a higher voltage or current is needed to drive the actuator, asimple op-amp would be sufficient which will consume very little extrapower other than to drive the actuator. The additional power could comefrom another modulated source or a DC frequency in the light signal.

An embodiment of the present invention will now be described in moredetail and with reference to the following Figures:

FIG. 1 shows the possible locations of an ear canal module and earimplant according to the present invention; and

FIG. 2 shows a block diagram identifying the components of the ear canalmodule and ear implant of the present invention.

FIG. 1 shows somewhat schematically the relative locations of theexternal ear canal module 1 and ear implant 20. As can be seen, the earmodule 1 is located in the ear canal 3. The ear module 1 has a channel 5through the module 1 in order to prevent occlusion of the ear canal 3. Amodulated IR light signal, represented by the dashed lines 7, is emittedby an LED 9, through the ear drum 11, so as to be detected by an implant20. In this embodiment, the implant 20 sits on the incudostapedialjoint, so as to oscillate the stapes, although the implant could belocated elsewhere, for example in the promontory.

FIG. 2 shows in more detail the components of the ear module 1 andimplant 20 of the present invention. The ear module 1 comprises amicrophone 11, and associated electronic circuiting 13 for transducingsound into an electrical signal which is in turn converted andtransmitted as the modulated light signal 7 (shown as broken arrows) bythe LED 9. Power for the ear module is provided by a battery 15. Themodulated light signal 7 passes through the ear drum 11 and is detectedby a photodiode 22 of implant 20. The photodiode 22 converts the lightsignal 7 into an electrical signal for driving/oscillating a diskactuator 24 made of PZT piezo ceramic material.

Advantageously the hearing system features surgical simplicity, safetyand life-long durability (no implanted battery needs to be replaced),easy updating of signal processing (external module) algorithms, minimumor no deterioration (destruction) on the residual hearing level, minimumor no acoustic feedback and canal occlusion problems which are inherentwith conventional hearing aids, low-cost and acceptability for both thesurgeons and the patients.

To illustrate the efficacy of the present invention, the inventors havetested the feasibility of two components of the invention ie. theossicular mounted piezoelectric actuator and the infrared telemetrysystem.

We have tested the feasibility of the two key innovations in thisproject, i.e. the ossicular mounted piezoelectric actuator and theinfrared telemetry system.

(a) Ossicular mounted piezoelectric actuator. An ossicular mountedactuator is used in the Soundbridge implant [1], but it has anelectromagnetic actuator with a moving mass component, so the vibratingmechanism is not directly comparable with the presently proposed design.The piezoelectric actuator used for the pilot study was an 8 mm diametersingle layer disk bender, of the type used in the TICA hearing implant(2). The output vibration level of the TICA actuator is well documentedand has been shown clinically to satisfy the requirements of a hearingimplant [2]. This makes it suitable for demonstrating the ossicularmounted concept. The actuator is available commercially (American PiezoCompany). Its total thickness is 0.22 mm and its mass is less than 150mg.

FIG. 3 shows a schematic of the test configuration, which was designedto be a more demanding load than the real ossicular chain. A copper wirewas used to simulate the ossicular chain. It was glued at one end to a17 mm long section of flexible plastic sleeving (polyolefin, 12.7 mmbore, 0.3 mm thick, weight 0.36 g), giving a crude representation of theeardrum. The wire weighed 60 mg, which is about 10% heavier than theossicular chain [3]. The other side of the tube was glued to a solidframework. The wire passed through the centre of the actuator, with atight fit to hold it in place. The protruding wire weighed about 8 mg,twice the weight of the stapes. Reference data were obtained for anunloaded actuator, which was attached around its circumference to asolid framework, FIG. 3(b). Vibration was measured with a laservibrometer. FIG. 4 shows the measured displacements.

The TICA is reported as producing 22 nm at 2.83V peak to peak [2], whichwas found to be equivalent to around 100 dB SPL at 1 kHz and more than130 dB SPL (Sound Pressure Level) at higher frequencies [2]. The‘ossicular mounted’ actuator of the present invention gave a nearly flatresponse of 47 nm below 4 kHz at 1V excitation, considerably higher thanthe TICA, and a similar resonant frequency of 7-10 kHz.

(b) Infrared light transmission. Light transmission was tested through achicken skin, which is more opaque than the eardrum and at least twiceas thick. The simulation was otherwise as realistic as possible, interms of the likely size of the light emitting diode (LED) source andthe distances for the light path. The energy detected by a photodiodewas used to drive the disk bender actuator and could produce a vibrationdisplacement level equivalent to 100 dB SPL, which is more than adequatefor an implant, using 2.1 mW optical power. A custom made actuator isenvisaged to perform much better. The level of infrared energy used wasless than 1% of the level that could cause tissue damage, according toBritish Standard EN 60825-1: 1994 Safety of Laser Products. Thisdemonstrates the viability of the trans-eardrum telemetry concept.

REFERENCES

-   [1] Lenarz T, Weber B P, Mack K F, Battmer R D, Gnadeberg D. The    Vibrant Soundbridge System: a new kind of hearing aid for    sensorineural hearing loss. 1: Function and initial clinical    experiences. Laryngorhinootologie. 1998; 77: 247-55. (In German).-   [2] Zenner H P, Leysieffer H, Maassen M, et al. Human Studies of a    Piezoelectric Transducer and a Microphone for a Totally Implantable    Electronic Hearing Device. American Journal of Otology, 2000; 21:    196-204.-   [3] Kirkae I. The structure and function of the middle ear.    University of Tokyo Press, Tokyo, 1960.

1. A hearing aid system comprising an external ear canal module (1) and an implant (20); the external ear canal module (1) comprising a microphone (11), a light source (9), a power source (15) and necessary electronic circuitry; the implant (20) comprising a photoreceiver (21) actively coupled to a hearing actuator (24); and wherein in use, sound detected by the microphone (11) of the external ear canal module (1) is converted and transmitted by the light source (9) as a modulated light signal (7), the modulated light signal being detected by the photoreceiver (22) of the implant and converted to an electrical signal for driving the hearing actuator (24).
 2. The hearing aid system according to claim 1 wherein the modulated light signal (7) provides the sound information and optionally power for the ear implant (20).
 3. The hearing aid system according to claim 1 wherein a further light source is provided to charge a battery within the ear implant (20), the battery serving to provide additional power to the implant (20).
 4. The hearing aid system according to claim 1 wherein the components of the external ear canal module (1) are contained within a single housing which is shaped to fit within the external ear canal.
 5. The hearing aid system according to claim 1 wherein the light source (9) is a light emitting diode (LED).
 6. The hearing aid system according to claim 1 wherein the light signal (7) is near infrared (NIR) light or infrared (1R) energy.
 7. The hearing aid system according to claim 1 wherein a channel, valve or the like is provided in the module (1) so as to provide a passage through the module (1) thereby preventing blockage of the ear canal.
 8. The hearing aid system according to claim 1 wherein the implant (20) is an integrated photoreceiver/actuator unit.
 9. The hearing aid system according to claim 8 wherein the integrated photoreceiver actuator unit is a micro electromechanical system (MEMS)—integrated photoreceiver/actuator.
 10. The hearing aid system according to claim 1 wherein the photoreceiver is a photo-sensitive diode or photovoltaic cell.
 11. The hearing aid system according to any preceding claim 1 wherein the actuator (24) is arranged in use to contact the ossicular chain.
 12. The hearing aid system according to claim 11 wherein the actuator (24) is located on the incus long process, the incodostapedial joint or the stapes.
 13. The hearing aid system according to claim 11 wherein the actuator (24) is arranged in use to be positioned in the middle ear.
 14. The hearing aid system according to claim 11 wherein the actuator is secured in place by cementing, grafting or by mechanical means.
 15. The hearing aid system according to claim 1 wherein actuation of the middle or inner ear compounds is by mechanically or electrical means.
 16. The hearing aid system according to claim 15 wherein actuation is by mechanical means, wherein the actuator is in the form of a thin disk or disk mode of piezo ceramic material.
 17. The hearing aid system according to claim 16 wherein the piezo ceramic material is lead zirconate titanate (PZT) or PLZT.
 18. The hearing aid system according to claim 15 wherein actuation is by mechanical means, wherein the actuator comprises a flexible diaphragm.
 19. A method of powering and/or signalling an ear implant comprising transmitting a light source, or sources through a patient's ear drum, such that said light source(s) is/are received by the ear implant and wherein said light source(s) is/are capable of powering and/or signalling the ear implant.
 20. The hearing aid system according to claim 1 wherein the implant is located in the body side of the eardrum. 